The United Nations Treaty Collection recently redesigned their website. The site is a great source for finding out the status of recent treaties as well as being an access point for treaties already in existence.
NYU Libraries provide a link through the "Articles via Databases" page. Once there just go to "U".
In particular, you can now search through the UN Treaty Series by name, title or participant. The site also provides access to the League of Nations Treaty Series.
Because the site is so new, please be advised that it still has some bugs so do check back if its not working properly. Once those are fixed it looks like it will be a welcome page for anyone researching UN Treaties.